Throughout the episode Simon and Marcy, you see what appears to be pink gum all over the place. At the end of the episode we find out that this gum is alive and even sentient. It helps out Simon in little ways here and there, where it can. It serves as a latter (even though I'm sure it was probably just there already, it's still a happy coincidence that it was there for him) when he wants to investigate the food truck and had no other way of getting up there. It is also within earshot (or whatever it uses for hearing) when Simon says that he needs chicken soup. Then it tries to catch him when he jumps from that raised area. Even though he would have been zombie bait if he had stayed there, he was able to escape from it and in doing so it lessened how far he would have fallen, thus helping him. Then when he's about to run into a dead end, it helps him again (happy coincidence or not) by doing what it can in trapping some of the zombie-mutants. After all is quiet and Simon regains his self, he notices that the gum has now appeared in the ally a few feet away, and has brought him, not only a can of chicken soup, but a swiss army knife with the can opener and spoon sticking out of it. Now, even if all the other times were coincidences and that it just happened to be there, why would this possible first candy person go through the trouble of finding such things in a city where everything is gone (so it would have been pretty hard to find) just for this stranger that walked in, and is clearly happy to do so? Maybe it's because he isn't a stranger. If you've read my Betty/PB Theory, you know that I believe that Betty is Princess Bubblegum. (if you haven't, please go check it out so you may understand this theory better. [link]
I theorize that this sentient gum is either a prototype candy person that was made by Betty to watch over Simon while she herself can stay safe, or is Betty herself, in a raw form after having become Bubblegum, if something had gone wrong. (although I'm more partial to the first, you can side with whichever one makes more sense to you)
I do not own Adventure Time or its characters. The above image is screenshots I took from the episode to help illustrate my theory.